Answer:
Let the original price of one book be x. Then, the sale price of one book is x - 5.
The total cost of 5 books at the sale price is 5(x - 5) = 5x - 25.
The cost of 4 books at the original price is 4x.
According to the problem, the total cost of 5 books at the sale price is $2 more than the cost of 4 books at the original price:
5x - 25 = 4x + 2
Solving for x, we get:
x = 27
Therefore, the original price of one book is $27.